It is known that in crochet galloon machines for warp knitting, such as crochet galloon looms of the type described in EP0393297, formation of the article of manufacture takes place at a front grooved bar having a horizontal extension and being rigidly supported, at the respective opposite ends, between two side posts being part of the machine base. Operating on the front grooved bar is a plurality of needles disposed consecutively in side by side relationship and simultaneously operated in a reciprocating motion in the direction of their longitudinal extension. A plurality of eye-pointed needles disposed consecutively in side by side relationship operate in front of the needles; they are parallel to the front grooved bar and supported by a guide bar engaged by means of the posts with possibility of sliding and carrying out angular oscillation on the longitudinal extension axis thereof. The guide bar is submitted to the combined action of transverse actuating means giving the eye-pointed needles a reciprocating motion in a direction parallel to the front grooved bar, as well as of angular oscillation means by effect of which the ends of the eye-pointed needles carry out a reciprocating motion in a substantially vertical direction, by alternately moving to a higher level and a lower level relative to the needles themselves.
Movements of the needles and the eye-pointed needles are synchronised in such a manner that when the needles are in a forward or advanced position towards the eye-pointed needles, the latter are in a raised position and carry out a translation motion, each moving from one side to the other of at least one respective needle. During this step the warp yarn of each eye-pointed needle is disposed on either side of the needle, so that it engages in the hooked portion provided on the end of the needle itself.
When the needles move backwards from the forward position, the warp yarn engaged in the hooked portion of each needle forms a loop that is guided through the loop of the knitting stitch formed in the preceding operating cycle, while the stitch itself, retained by the front grooved bar, is discharged from the needle end when said needle is about to reach the end of stroke of the back-moving step. Meanwhile, the eye-pointed needles are brought to a slightly lower level than the needles. When the needles are about to be brought back to the forward position, the eye-pointed needles are horizontally translated in a direction opposite to the horizontal movement previously carried out, so that the warp yarns form new knitting stitches sliding along the needles during the moving forward step. When the needles come close to the forward position again, the eye-pointed needles go back to a slightly higher level than said needles to give rise to a new knitting cycle.
Co-operation between needles and eye-pointed needles gives rise to a sequence of knitting stitches, forming a plurality of parallel chains moving little by little downwards from the front grooved bar.
The chains are further interlaced with the weft yarns carried by respective threading tubes operating above the needles, and disposed consecutively in side by side relationship, parallel to the front grooved bar. The threading tubes are supported by one or more carrier slide bars the opposite ends of which are slidably guided through lifting plates in turn slidably engaged in a vertical direction on the base posts.
Each carrier slide bar is submitted to the action of respective horizontal actuating means giving each threading tube a reciprocating motion parallel to the extension of the front grooved bar. The carrier slide bars are further simultaneously operated with a reciprocating oscillation in a vertical direction, upon command of a kinematic mechanism acting on the lifting plates.
Operation of the carrier slide bars is co-ordinated with that of the needles and the eye-pointed needles, so that each weft yarn is selectively laid on either side of one or more needles to pass below said needles when they reach the return end of stroke and start the advancing motion towards the eye-pointed needles again.
The weft yarn placed under the needles will be interknitted with the knitting stitches formed by the warp yarns in the subsequent operating cycle.
After the above statements, it is to be pointed out that within the field concerning development and improvement of the textile machines, in order to face the increasing market requirements, many efforts are spent in an attempt to increase productivity of the machines themselves and complexity of the articles of manufacture produced by them.
It is also to be pointed out that one of the greatest limitations is presently represented by the maximum number of carrier slide bars disposed in a fan-shaped conformation between the lifting plates to cause the ends of the respective threading tubes to converge as much as possible towards a common alignment direction.
Based on the above considerations it has been found that presently the greatest constraints to productivity of the crochet galloon machines is due to the fact that, to equip the machines with a great number of carrier slide bars, greater than sixteen, it is necessary to use very long needles projecting in overhanging from the needle bar, in order to enable them to reach all threading tubes without the needle bar interfering with the front grooved bar.
In fact, due to said important length, during reciprocation at high speed along their longitudinal extension, the needles would inevitably tend to bend.
These bending deformations bring to an inexact positioning of the individual needles relative to the threading tubes and the eye-pointed needles, and sometimes even to mechanical interferences with consequent risks of damaging and/or breaking these components.